This invention relates to electrical interconnects, and more particularly, to high density electrical make/break interconnects such as used in thermal ink jet printers with replaceable print cartridges.
Printers are devices that print images onto a printing medium such as a sheet of paper. Printers of many types are available, and are commonly linked to a computer that supplies the content of the images, in the form of text, characters, or figures, that are to be printed.
An ink jet printer forms small droplets of a colorant such as an ink or a dye that are ejected toward the printing medium in the pattern that forms the images. Ink jet printers are fast, producing a high output of print, and quiet, because there is no mechanical impact dring formation of the image, other than the deposition of the ink onto the medium.
One type of ink jet printer, the thermal ink jet printer, has a large number of individual colorant-ejection nozzles in a print head, oriented in a facing, but spaced-apart, relationship to the printing medium. There is an electrical resistor adjacent each nozzle, and a pulse of current through the resistor causes ejection of a droplet of colorant form the nozzle toward the medium. The print head moves relative to the surface of the medium, with the nozzles ejecting droplets of colorant under command at the proper times. (Alternatively, for a large printing array the print head may be stationary.) The droplets strike the medium and then dry to form "dots" of colorant that, when view together, create the permanently printed image.
Most thermal ink jet printers are constructed with a permanent printer body and a printing means. The printing mechanism includes, preferably, a disposable print head cartridge containing both the colorant ejector and the colorant supply (or, alternatively, a permanent colorant ejector with a disposable colorant supply). The printer body contains the mechanisms to support the printing medium and the print head cartridge in the proper facing relationship so that printing can be accomplished, the power supply that supplies the electrical current to the ejector resistors, the electronic controllers to achieve particular printing functions, and the interface to the computer. The disposable print head cartridge includes the ejector mechanism, its support, and in some cases the colorant supply. There must be a make/break interconnect between the printer body and the disposable print head cartridge, which is a connection that is readily made, is "temporary" in the sense that it is maintained until the cartridge is to be replaced, and allows easy disconnection and replacement. The present invention is concerned with such a make/break interconnect.
The earliest commercial thermal ink jet print heads had a relatively small number of nozzles, typically about 12 nozzles. There is, however, a strong incentive to increase the number of operable nozzles in the print head and to space them very closely together, since the closer the nozzles are to each other the more perfect the appearance of the images. That is, when the nozzles are far apart, the images appear to the eye to be made of a series of dots, but when the nozzles are closely spaced, the dotlike character of the images is not apparent to the eye. It is preferable that the makeup of the image as a collection of dots not be discernible, and that the image appear to be continuous.
The nozzles and related portions of the print head are made by techniques similar to those used in the microelectronics industry, and can be made with very small spacings. However, a practical obstacle to the desired reduction of spacing between the nozzles is the need to transmit appropriate electrical control signals to the resistor for each nozzle. There must be at least one electrical conduction path for each resistor from the power supply in the printer body, into the disposable print head cartridge, and thence to the nozzle. It has been found that, for large numbers of nozzles and required interconnects, and with an essentially constant size of print head, there is simply insufficient room to form all of the make/break interconnections between the disposable cartridge and the printer body.
One approach to this problem of providing a large number of interconnections has been to make each individual interconnection smaller. This approach is limited, however, by manufacturing tolerances and the realization that the replacement of the cartridge is performed by an untrained user of the printer, not a highly trained specialist. The miniaturization of the interconnects cannot be pushed to the point that slight errors made during the replacement procedure cause the printer to become inoperable.
Thus, there is a continuing need for improved ink jet printers wherein larger numbers of nozzles can be provided in a disposable print head cartridge, yet interconnects between the cartridge and the body of the printer can be made easily by the user. The present invention fulfills this need, and further provides related advantages.